Azo dyes have numerous excellent properties such as high dyeing property, fastness to heat, light, and washing, and low production cost, and thus have been hitherto used widely for dyeing of textile fibers (e.g. cotton, wool, and synthetic fiber), leather, paper, plastic, fur, etc., and for food. At present, in addition to those conventional applications, the azo dyes are used for a paint pigment, for an ink, for inkjet printing, for laser printing, for copying, for image formation by heat-sensitive transfer system, for an optical recording material, for an organic EL luminescent material, for laser, for an organic semiconductor, for a solar cell, for a fluorescent probe, for a nonlinear optical material, for various filters for a solid pickup tube etc., for a display such as a color LCD, for a hair dye, and the like. The azo dye has a dye skeleton most widely used. Industrial Dyes: Chemistry, Properties, Applications (edited by K. Hunger, published by Wiley-VCH, 2003) describes extensively specific application examples of the azo dyes.
However, the azo dyes are known to form aromatic amine compounds when they are metabolized reductively in a living body or organisms, and concerns over their safety has been pointed out recently (see R. K. Lynn et al., Toxicol. Appl. Pharmacol., vol. 56, p. 248, 1980, for example). In consideration of influences in a living body, development of hardly reducible azo dyes has been required.
Synthesis of a novel heterocyclic compound having an azo group in a ring, that is, a 1,10-heterodisubstituted benzo[c]cinnoline derivative has been reported recently (see V. Benin et al., J. Org. Chem., vol. 65, p. 6388, 2000, for example). However, the report focuses on a mechanism of a ring formation reaction and discussion of structural chemistry.